1. Field of the Invention
Embodiments of the invention relate to the fields of nondestructive inspection (NDI) and/or nondestructive testing (NDT) of substrates for corrosion. Preferably embodiments relate to a process for creation of discrete corrosion defects on substrates and to creation of standards for NDI and NDT. Hereinafter “NDT” will refer to uses for both NDI and NDT, unless otherwise indicated.
2. Background
Painted or coated substrates, including those substrates constructed from traditional steel and aluminum alloys as well as more modern composite and sandwich structures, present particular challenge for analysis by traditional NDT methods. For convenience, and unless otherwise noted, “paint” shall be used herein to refer to both paints and coatings when used as any part of speech. For painted parts or components, corrosion does not generally become evident until it has progressed far enough to disrupt the integrity of the paint. If the paint has not been disrupted but corrosion is still suspected to have begun at the surface of the substrate, identification of corrosion has required removal of the paint or other coating. Some methods that may be used to detect corrosion, such as hammering an area and listening for sounds characteristic of possible corrosion, is subjective and may be unreliable and/or may require a high amount of training and skill.
Whether the corrosion is discovered following disruption of the paint or after intentional removal of the paint, the paint must be removed and the substrate/substructure repaired and repainted after the corrosion damage has been repaired. Paint removal and replacement results in significant downtime, and it can generate significant hazardous waste, such as volatile chemicals and air pollutants.
It would be desirable to develop NDT corrosion test standards which emulate specific substrates, coatings, and substrate orientations for each application of interest. These NDT corrosion test standards could provide benchmarks for calibration of NDT systems, providing reliable and reproducible results for indicating corrosion damage and delineating corrosion damage from other mechanical defects under paint.